We are first time chicken owners. The hens have started laying a few weeks ago and we are up to 8 eggs a day now! My husband built a great coop for our 8 mix-of-breeds hens. See picture. The problem is that they don't go inside to roost, they all huddles jammed together on the side outside area (protected) on the level as the indoor area. Besides a couple of them, when they were around 10 weeks old, they all sleep outside. They go in the coop to the laying area and lay eggs, they will not sleep inside (penty of nice areas to roost, a 5 times as large.) I am in MN, besides a few hot days, we have been in the 70s durning the day and lower 60s at night. The coop is clean, has the entry door and even a plexiglass skylight. They basically (all 8) are on top of each other when they sleep on the outside/side of the coop.

What is wrong? They seems happy and healthy. The coop has ventilation and sometimes even latch the egg area open for more air flow. Advice?